libexec/tftpd/tftpd.c

   1 /*
   2  * Copyright (c) 1983, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  * @(#) Copyright (c) 1983, 1993 The Regents of the University of California.  All rights reserved.
  34  * @(#)tftpd.c  8.1 (Berkeley) 6/4/93
  35  * $FreeBSD: src/libexec/tftpd/tftpd.c,v 1.15.2.5 2003/04/06 19:42:56 dwmalone Exp $
  36  * $DragonFly: src/libexec/tftpd/tftpd.c,v 1.3 2003/11/20 14:32:17 eirikn Exp $
  37  */
  38
  39 /*
  40  * Trivial file transfer protocol server.
  41  *
  42  * This version includes many modifications by Jim Guyton
  43  * <guyton@rand-unix>.
  44  */
  45
  46 #include <sys/param.h>
  47 #include <sys/ioctl.h>
  48 #include <sys/stat.h>
  49 #include <sys/socket.h>
  50 #include <sys/types.h>
  51
  52 #include <netinet/in.h>
  53 #include <arpa/tftp.h>
  54 #include <arpa/inet.h>
  55
  56 #include <ctype.h>
  57 #include <errno.h>
  58 #include <fcntl.h>
  59 #include <libutil.h>
  60 #include <netdb.h>
  61 #include <pwd.h>
  62 #include <setjmp.h>
  63 #include <signal.h>
  64 #include <stdio.h>
  65 #include <stdlib.h>
  66 #include <string.h>
  67 #include <syslog.h>
  68 #include <unistd.h>
  69
  70 #include "tftpsubs.h"
  71
  72 #define TIMEOUT         5
  73 #define MAX_TIMEOUTS    5
  74
  75 int     peer;
  76 int     rexmtval = TIMEOUT;
  77 int     max_rexmtval = 2*TIMEOUT;
  78
  79 #define PKTSIZE SEGSIZE+4
  80 char    buf[PKTSIZE];
  81 char    ackbuf[PKTSIZE];
  82 struct  sockaddr_storage from;
  83 int     fromlen;
  84
  85 void    tftp(struct tftphdr *, int);
  86 static void unmappedaddr(struct sockaddr_in6 *);
  87
  88 /*
  89  * Null-terminated directory prefix list for absolute pathname requests and
  90  * search list for relative pathname requests.
  91  *
  92  * MAXDIRS should be at least as large as the number of arguments that
  93  * inetd allows (currently 20).
  94  */
  95 #define MAXDIRS 20
  96 static struct dirlist {
  97         const char      *name;
  98         int     len;
  99 } dirs[MAXDIRS+1];
 100 static int      suppress_naks;
 101 static int      logging;
 102 static int      ipchroot;
 103
 104 static const char *errtomsg(int);
 105 static void  nak(int);
 106 static void  oack(void);
 107
 108 static void  timer(int);
 109 static void  justquit(int);
 110
 111 int
 112 main(int argc, char *argv[])
 113 {
 114         struct tftphdr *tp;
 115         int n;
 116         int ch, on;
 117         struct sockaddr_storage me;
 118         int len;
 119         char *chroot_dir = NULL;
 120         struct passwd *nobody;
 121         const char *chuser = "nobody";
 122
 123         openlog("tftpd", LOG_PID | LOG_NDELAY, LOG_FTP);
 124         while ((ch = getopt(argc, argv, "cClns:u:")) != -1) {
 125                 switch (ch) {
 126                 case 'c':
 127                         ipchroot = 1;
 128                         break;
 129                 case 'C':
 130                         ipchroot = 2;
 131                         break;
 132                 case 'l':
 133                         logging = 1;
 134                         break;
 135                 case 'n':
 136                         suppress_naks = 1;
 137                         break;
 138                 case 's':
 139                         chroot_dir = optarg;
 140                         break;
 141                 case 'u':
 142                         chuser = optarg;
 143                         break;
 144                 default:
 145                         syslog(LOG_WARNING, "ignoring unknown option -%c", ch);
 146                 }
 147         }
 148         if (optind < argc) {
 149                 struct dirlist *dirp;
 150
 151                 /* Get list of directory prefixes. Skip relative pathnames. */
 152                 for (dirp = dirs; optind < argc && dirp < &dirs[MAXDIRS];
 153                      optind++) {
 154                         if (argv[optind][0] == '/') {
 155                                 dirp->name = argv[optind];
 156                                 dirp->len  = strlen(dirp->name);
 157                                 dirp++;
 158                         }
 159                 }
 160         }
 161         else if (chroot_dir) {
 162                 dirs->name = "/";
 163                 dirs->len = 1;
 164         }
 165         if (ipchroot && chroot_dir == NULL) {
 166                 syslog(LOG_ERR, "-c requires -s");
 167                 exit(1);
 168         }
 169
 170         on = 1;
 171         if (ioctl(0, FIONBIO, &on) < 0) {
 172                 syslog(LOG_ERR, "ioctl(FIONBIO): %m");
 173                 exit(1);
 174         }
 175         fromlen = sizeof (from);
 176         n = recvfrom(0, buf, sizeof (buf), 0,
 177             (struct sockaddr *)&from, &fromlen);
 178         if (n < 0) {
 179                 syslog(LOG_ERR, "recvfrom: %m");
 180                 exit(1);
 181         }
 182         /*
 183          * Now that we have read the message out of the UDP
 184          * socket, we fork and exit.  Thus, inetd will go back
 185          * to listening to the tftp port, and the next request
 186          * to come in will start up a new instance of tftpd.
 187          *
 188          * We do this so that inetd can run tftpd in "wait" mode.
 189          * The problem with tftpd running in "nowait" mode is that
 190          * inetd may get one or more successful "selects" on the
 191          * tftp port before we do our receive, so more than one
 192          * instance of tftpd may be started up.  Worse, if tftpd
 193          * break before doing the above "recvfrom", inetd would
 194          * spawn endless instances, clogging the system.
 195          */
 196         {
 197                 int pid;
 198                 int i, j;
 199
 200                 for (i = 1; i < 20; i++) {
 201                     pid = fork();
 202                     if (pid < 0) {
 203                                 sleep(i);
 204                                 /*
 205                                  * flush out to most recently sent request.
 206                                  *
 207                                  * This may drop some request, but those
 208                                  * will be resent by the clients when
 209                                  * they timeout.  The positive effect of
 210                                  * this flush is to (try to) prevent more
 211                                  * than one tftpd being started up to service
 212                                  * a single request from a single client.
 213                                  */
 214                                 j = sizeof from;
 215                                 i = recvfrom(0, buf, sizeof (buf), 0,
 216                                     (struct sockaddr *)&from, &j);
 217                                 if (i > 0) {
 218                                         n = i;
 219                                         fromlen = j;
 220                                 }
 221                     } else {
 222                                 break;
 223                     }
 224                 }
 225                 if (pid < 0) {
 226                         syslog(LOG_ERR, "fork: %m");
 227                         exit(1);
 228                 } else if (pid != 0) {
 229                         exit(0);
 230                 }
 231         }
 232
 233         /*
 234          * Since we exit here, we should do that only after the above
 235          * recvfrom to keep inetd from constantly forking should there
 236          * be a problem.  See the above comment about system clogging.
 237          */
 238         if (chroot_dir) {
 239                 if (ipchroot) {
 240                         char *tempchroot;
 241                         struct stat sb;
 242                         int statret;
 243                         struct sockaddr_storage ss;
 244                         char hbuf[NI_MAXHOST];
 245
 246                         memcpy(&ss, &from, from.ss_len);
 247                         unmappedaddr((struct sockaddr_in6 *)&ss);
 248                         getnameinfo((struct sockaddr *)&ss, ss.ss_len,
 249                                     hbuf, sizeof(hbuf), NULL, 0,
 250                                     NI_NUMERICHOST | NI_WITHSCOPEID);
 251                         asprintf(&tempchroot, "%s/%s", chroot_dir, hbuf);
 252                         statret = stat(tempchroot, &sb);
 253                         if ((sb.st_mode & S_IFDIR) &&
 254                             (statret == 0 || (statret == -1 && ipchroot == 1)))
 255                                 chroot_dir = tempchroot;
 256                 }
 257                 /* Must get this before chroot because /etc might go away */
 258                 if ((nobody = getpwnam(chuser)) == NULL) {
 259                         syslog(LOG_ERR, "%s: no such user", chuser);
 260                         exit(1);
 261                 }
 262                 if (chroot(chroot_dir)) {
 263                         syslog(LOG_ERR, "chroot: %s: %m", chroot_dir);
 264                         exit(1);
 265                 }
 266                 chdir( "/" );
 267                 setuid(nobody->pw_uid);
 268                 setgroups(1, &nobody->pw_gid);
 269         }
 270
 271         len = sizeof(me);
 272         if (getsockname(0, (struct sockaddr *)&me, &len) == 0) {
 273                 switch (me.ss_family) {
 274                 case AF_INET:
 275                         ((struct sockaddr_in *)&me)->sin_port = 0;
 276                         break;
 277                 case AF_INET6:
 278                         ((struct sockaddr_in6 *)&me)->sin6_port = 0;
 279                         break;
 280                 default:
 281                         /* unsupported */
 282                         break;
 283                 }
 284         } else {
 285                 memset(&me, 0, sizeof(me));
 286                 me.ss_family = from.ss_family;
 287                 me.ss_len = from.ss_len;
 288         }
 289         alarm(0);
 290         close(0);
 291         close(1);
 292         peer = socket(from.ss_family, SOCK_DGRAM, 0);
 293         if (peer < 0) {
 294                 syslog(LOG_ERR, "socket: %m");
 295                 exit(1);
 296         }
 297         if (bind(peer, (struct sockaddr *)&me, me.ss_len) < 0) {
 298                 syslog(LOG_ERR, "bind: %m");
 299                 exit(1);
 300         }
 301         if (connect(peer, (struct sockaddr *)&from, from.ss_len) < 0) {
 302                 syslog(LOG_ERR, "connect: %m");
 303                 exit(1);
 304         }
 305         tp = (struct tftphdr *)buf;
 306         tp->th_opcode = ntohs(tp->th_opcode);
 307         if (tp->th_opcode == RRQ || tp->th_opcode == WRQ)
 308                 tftp(tp, n);
 309         exit(1);
 310 }
 311
 312 struct formats;
 313 int     validate_access(char **, int);
 314 void    xmitfile(struct formats *);
 315 void    recvfile(struct formats *);
 316
 317 struct formats {
 318         const char      *f_mode;
 319         int     (*f_validate)(char **, int);
 320         void    (*f_send)(struct formats *);
 321         void    (*f_recv)(struct formats *);
 322         int     f_convert;
 323 } formats[] = {
 324         { "netascii",   validate_access,        xmitfile,       recvfile, 1 },
 325         { "octet",      validate_access,        xmitfile,       recvfile, 0 },
 326 #ifdef notdef
 327         { "mail",       validate_user,          sendmail,       recvmail, 1 },
 328 #endif
 329         { 0,            NULL,                   NULL,           NULL,     0 }
 330 };
 331
 332 struct options {
 333         const char      *o_type;
 334         char    *o_request;
 335         int     o_reply;        /* turn into union if need be */
 336 } options[] = {
 337         { "tsize",      NULL, 0 },              /* OPT_TSIZE */
 338         { "timeout",    NULL, 0 },              /* OPT_TIMEOUT */
 339         { NULL,         NULL, 0 }
 340 };
 341
 342 enum opt_enum {
 343         OPT_TSIZE = 0,
 344         OPT_TIMEOUT,
 345 };
 346
 347 /*
 348  * Handle initial connection protocol.
 349  */
 350 void
 351 tftp(struct tftphdr *tp, int size)
 352 {
 353         char *cp;
 354         size_t i;
 355         int first = 1, has_options = 0, ecode;
 356         struct formats *pf;
 357         char *filename, *mode = NULL, *option, *ccp;
 358         char fnbuf[MAXPATHLEN];
 359
 360         cp = tp->th_stuff;
 361 again:
 362         while (cp < buf + size) {
 363                 if (*cp == '\0')
 364                         break;
 365                 cp++;
 366         }
 367         if (*cp != '\0') {
 368                 nak(EBADOP);
 369                 exit(1);
 370         }
 371         i = cp - tp->th_stuff;
 372         if (i >= sizeof(fnbuf)) {
 373                 nak(EBADOP);
 374                 exit(1);
 375         }
 376         memcpy(fnbuf, tp->th_stuff, i);
 377         fnbuf[i] = '\0';
 378         filename = fnbuf;
 379         if (first) {
 380                 mode = ++cp;
 381                 first = 0;
 382                 goto again;
 383         }
 384         for (cp = mode; *cp; cp++)
 385                 if (isupper(*cp))
 386                         *cp = tolower(*cp);
 387         for (pf = formats; pf->f_mode; pf++)
 388                 if (strcmp(pf->f_mode, mode) == 0)
 389                         break;
 390         if (pf->f_mode == 0) {
 391                 nak(EBADOP);
 392                 exit(1);
 393         }
 394         while (++cp < buf + size) {
 395                 for (i = 2, ccp = cp; i > 0; ccp++) {
 396                         if (ccp >= buf + size) {
 397                                 /*
 398                                  * Don't reject the request, just stop trying
 399                                  * to parse the option and get on with it.
 400                                  * Some Apple OpenFirmware versions have
 401                                  * trailing garbage on the end of otherwise
 402                                  * valid requests.
 403                                  */
 404                                 goto option_fail;
 405                         } else if (*ccp == '\0')
 406                                 i--;
 407                 }
 408                 for (option = cp; *cp; cp++)
 409                         if (isupper(*cp))
 410                                 *cp = tolower(*cp);
 411                 for (i = 0; options[i].o_type != NULL; i++)
 412                         if (strcmp(option, options[i].o_type) == 0) {
 413                                 options[i].o_request = ++cp;
 414                                 has_options = 1;
 415                         }
 416                 cp = ccp-1;
 417         }
 418
 419 option_fail:
 420         if (options[OPT_TIMEOUT].o_request) {
 421                 int to = atoi(options[OPT_TIMEOUT].o_request);
 422                 if (to < 1 || to > 255) {
 423                         nak(EBADOP);
 424                         exit(1);
 425                 }
 426                 else if (to <= max_rexmtval)
 427                         options[OPT_TIMEOUT].o_reply = rexmtval = to;
 428                 else
 429                         options[OPT_TIMEOUT].o_request = NULL;
 430         }
 431
 432         ecode = (*pf->f_validate)(&filename, tp->th_opcode);
 433         if (has_options)
 434                 oack();
 435         if (logging) {
 436                 char hbuf[NI_MAXHOST];
 437
 438                 getnameinfo((struct sockaddr *)&from, from.ss_len,
 439                             hbuf, sizeof(hbuf), NULL, 0,
 440                             NI_WITHSCOPEID);
 441                 syslog(LOG_INFO, "%s: %s request for %s: %s", hbuf,
 442                         tp->th_opcode == WRQ ? "write" : "read",
 443                         filename, errtomsg(ecode));
 444         }
 445         if (ecode) {
 446                 /*
 447                  * Avoid storms of naks to a RRQ broadcast for a relative
 448                  * bootfile pathname from a diskless Sun.
 449                  */
 450                 if (suppress_naks && *filename != '/' && ecode == ENOTFOUND)
 451                         exit(0);
 452                 nak(ecode);
 453                 exit(1);
 454         }
 455         if (tp->th_opcode == WRQ)
 456                 (*pf->f_recv)(pf);
 457         else
 458                 (*pf->f_send)(pf);
 459         exit(0);
 460 }
 461
 462
 463 FILE *file;
 464
 465 /*
 466  * Validate file access.  Since we
 467  * have no uid or gid, for now require
 468  * file to exist and be publicly
 469  * readable/writable.
 470  * If we were invoked with arguments
 471  * from inetd then the file must also be
 472  * in one of the given directory prefixes.
 473  * Note also, full path name must be
 474  * given as we have no login directory.
 475  */
 476 int
 477 validate_access(char **filep, int mode)
 478 {
 479         struct stat stbuf;
 480         int     fd;
 481         struct dirlist *dirp;
 482         static char pathname[MAXPATHLEN];
 483         char *filename = *filep;
 484
 485         /*
 486          * Prevent tricksters from getting around the directory restrictions
 487          */
 488         if (strstr(filename, "/../"))
 489                 return (EACCESS);
 490
 491         if (*filename == '/') {
 492                 /*
 493                  * Allow the request if it's in one of the approved locations.
 494                  * Special case: check the null prefix ("/") by looking
 495                  * for length = 1 and relying on the arg. processing that
 496                  * it's a /.
 497                  */
 498                 for (dirp = dirs; dirp->name != NULL; dirp++) {
 499                         if (dirp->len == 1 ||
 500                             (!strncmp(filename, dirp->name, dirp->len) &&
 501                              filename[dirp->len] == '/'))
 502                                     break;
 503                 }
 504                 /* If directory list is empty, allow access to any file */
 505                 if (dirp->name == NULL && dirp != dirs)
 506                         return (EACCESS);
 507                 if (stat(filename, &stbuf) < 0)
 508                         return (errno == ENOENT ? ENOTFOUND : EACCESS);
 509                 if ((stbuf.st_mode & S_IFMT) != S_IFREG)
 510                         return (ENOTFOUND);
 511                 if (mode == RRQ) {
 512                         if ((stbuf.st_mode & S_IROTH) == 0)
 513                                 return (EACCESS);
 514                 } else {
 515                         if ((stbuf.st_mode & S_IWOTH) == 0)
 516                                 return (EACCESS);
 517                 }
 518         } else {
 519                 int err;
 520
 521                 /*
 522                  * Relative file name: search the approved locations for it.
 523                  * Don't allow write requests that avoid directory
 524                  * restrictions.
 525                  */
 526
 527                 if (!strncmp(filename, "../", 3))
 528                         return (EACCESS);
 529
 530                 /*
 531                  * If the file exists in one of the directories and isn't
 532                  * readable, continue looking. However, change the error code
 533                  * to give an indication that the file exists.
 534                  */
 535                 err = ENOTFOUND;
 536                 for (dirp = dirs; dirp->name != NULL; dirp++) {
 537                         snprintf(pathname, sizeof(pathname), "%s/%s",
 538                                 dirp->name, filename);
 539                         if (stat(pathname, &stbuf) == 0 &&
 540                             (stbuf.st_mode & S_IFMT) == S_IFREG) {
 541                                 if ((stbuf.st_mode & S_IROTH) != 0) {
 542                                         break;
 543                                 }
 544                                 err = EACCESS;
 545                         }
 546                 }
 547                 if (dirp->name == NULL)
 548                         return (err);
 549                 *filep = filename = pathname;
 550         }
 551         if (options[OPT_TSIZE].o_request) {
 552                 if (mode == RRQ)
 553                         options[OPT_TSIZE].o_reply = stbuf.st_size;
 554                 else
 555                         /* XXX Allows writes of all sizes. */
 556                         options[OPT_TSIZE].o_reply =
 557                                 atoi(options[OPT_TSIZE].o_request);
 558         }
 559         fd = open(filename, mode == RRQ ? O_RDONLY : O_WRONLY|O_TRUNC);
 560         if (fd < 0)
 561                 return (errno + 100);
 562         file = fdopen(fd, (mode == RRQ)? "r":"w");
 563         if (file == NULL) {
 564                 return errno+100;
 565         }
 566         return (0);
 567 }
 568
 569 int     timeouts;
 570 jmp_buf timeoutbuf;
 571
 572 void
 573 timer(int sig __unused)
 574 {
 575         if (++timeouts > MAX_TIMEOUTS)
 576                 exit(1);
 577         longjmp(timeoutbuf, 1);
 578 }
 579
 580 /*
 581  * Send the requested file.
 582  */
 583 void
 584 xmitfile(struct formats *pf)
 585 {
 586         struct tftphdr *dp;
 587         struct tftphdr *ap;    /* ack packet */
 588         int size, n;
 589         volatile unsigned short block;
 590
 591         signal(SIGALRM, timer);
 592         dp = r_init();
 593         ap = (struct tftphdr *)ackbuf;
 594         block = 1;
 595         do {
 596                 size = readit(file, &dp, pf->f_convert);
 597                 if (size < 0) {
 598                         nak(errno + 100);
 599                         goto abort;
 600                 }
 601                 dp->th_opcode = htons((u_short)DATA);
 602                 dp->th_block = htons((u_short)block);
 603                 timeouts = 0;
 604                 (void)setjmp(timeoutbuf);
 605
 606 send_data:
 607                 {
 608                         int i, t = 1;
 609                         for (i = 0; ; i++){
 610                                 if (send(peer, dp, size + 4, 0) != size + 4) {
 611                                         sleep(t);
 612                                         t = (t < 32) ? t<< 1 : t;
 613                                         if (i >= 12) {
 614                                                 syslog(LOG_ERR, "write: %m");
 615                                                 goto abort;
 616                                         }
 617                                 }
 618                                 break;
 619                         }
 620                 }
 621                 read_ahead(file, pf->f_convert);
 622                 for ( ; ; ) {
 623                         alarm(rexmtval);        /* read the ack */
 624                         n = recv(peer, ackbuf, sizeof (ackbuf), 0);
 625                         alarm(0);
 626                         if (n < 0) {
 627                                 syslog(LOG_ERR, "read: %m");
 628                                 goto abort;
 629                         }
 630                         ap->th_opcode = ntohs((u_short)ap->th_opcode);
 631                         ap->th_block = ntohs((u_short)ap->th_block);
 632
 633                         if (ap->th_opcode == ERROR)
 634                                 goto abort;
 635
 636                         if (ap->th_opcode == ACK) {
 637                                 if (ap->th_block == block)
 638                                         break;
 639                                 /* Re-synchronize with the other side */
 640                                 (void) synchnet(peer);
 641                                 if (ap->th_block == (block -1))
 642                                         goto send_data;
 643                         }
 644
 645                 }
 646                 block++;
 647         } while (size == SEGSIZE);
 648 abort:
 649         (void) fclose(file);
 650 }
 651
 652 void
 653 justquit(int sig __unused)
 654 {
 655         exit(0);
 656 }
 657
 658
 659 /*
 660  * Receive a file.
 661  */
 662 void
 663 recvfile(struct formats *pf)
 664 {
 665         struct tftphdr *dp;
 666         struct tftphdr *ap;    /* ack buffer */
 667         int n, size;
 668         volatile unsigned short block;
 669
 670         signal(SIGALRM, timer);
 671         dp = w_init();
 672         ap = (struct tftphdr *)ackbuf;
 673         block = 0;
 674         do {
 675                 timeouts = 0;
 676                 ap->th_opcode = htons((u_short)ACK);
 677                 ap->th_block = htons((u_short)block);
 678                 block++;
 679                 (void) setjmp(timeoutbuf);
 680 send_ack:
 681                 if (send(peer, ackbuf, 4, 0) != 4) {
 682                         syslog(LOG_ERR, "write: %m");
 683                         goto abort;
 684                 }
 685                 write_behind(file, pf->f_convert);
 686                 for ( ; ; ) {
 687                         alarm(rexmtval);
 688                         n = recv(peer, dp, PKTSIZE, 0);
 689                         alarm(0);
 690                         if (n < 0) {            /* really? */
 691                                 syslog(LOG_ERR, "read: %m");
 692                                 goto abort;
 693                         }
 694                         dp->th_opcode = ntohs((u_short)dp->th_opcode);
 695                         dp->th_block = ntohs((u_short)dp->th_block);
 696                         if (dp->th_opcode == ERROR)
 697                                 goto abort;
 698                         if (dp->th_opcode == DATA) {
 699                                 if (dp->th_block == block) {
 700                                         break;   /* normal */
 701                                 }
 702                                 /* Re-synchronize with the other side */
 703                                 (void) synchnet(peer);
 704                                 if (dp->th_block == (block-1))
 705                                         goto send_ack;          /* rexmit */
 706                         }
 707                 }
 708                 /*  size = write(file, dp->th_data, n - 4); */
 709                 size = writeit(file, &dp, n - 4, pf->f_convert);
 710                 if (size != (n-4)) {                    /* ahem */
 711                         if (size < 0) nak(errno + 100);
 712                         else nak(ENOSPACE);
 713                         goto abort;
 714                 }
 715         } while (size == SEGSIZE);
 716         write_behind(file, pf->f_convert);
 717         (void) fclose(file);            /* close data file */
 718
 719         ap->th_opcode = htons((u_short)ACK);    /* send the "final" ack */
 720         ap->th_block = htons((u_short)(block));
 721         (void) send(peer, ackbuf, 4, 0);
 722
 723         signal(SIGALRM, justquit);      /* just quit on timeout */
 724         alarm(rexmtval);
 725         n = recv(peer, buf, sizeof (buf), 0); /* normally times out and quits */
 726         alarm(0);
 727         if (n >= 4 &&                   /* if read some data */
 728             dp->th_opcode == DATA &&    /* and got a data block */
 729             block == dp->th_block) {    /* then my last ack was lost */
 730                 (void) send(peer, ackbuf, 4, 0);     /* resend final ack */
 731         }
 732 abort:
 733         return;
 734 }
 735
 736 struct errmsg {
 737         int     e_code;
 738         const char      *e_msg;
 739 } errmsgs[] = {
 740         { EUNDEF,       "Undefined error code" },
 741         { ENOTFOUND,    "File not found" },
 742         { EACCESS,      "Access violation" },
 743         { ENOSPACE,     "Disk full or allocation exceeded" },
 744         { EBADOP,       "Illegal TFTP operation" },
 745         { EBADID,       "Unknown transfer ID" },
 746         { EEXISTS,      "File already exists" },
 747         { ENOUSER,      "No such user" },
 748         { EOPTNEG,      "Option negotiation" },
 749         { -1,           0 }
 750 };
 751
 752 static const char *
 753 errtomsg(int error)
 754 {
 755         static char ebuf[20];
 756         struct errmsg *pe;
 757         if (error == 0)
 758                 return "success";
 759         for (pe = errmsgs; pe->e_code >= 0; pe++)
 760                 if (pe->e_code == error)
 761                         return pe->e_msg;
 762         snprintf(ebuf, sizeof(buf), "error %d", error);
 763         return ebuf;
 764 }
 765
 766 /*
 767  * Send a nak packet (error message).
 768  * Error code passed in is one of the
 769  * standard TFTP codes, or a UNIX errno
 770  * offset by 100.
 771  */
 772 static void
 773 nak(int error)
 774 {
 775         struct tftphdr *tp;
 776         int length;
 777         struct errmsg *pe;
 778
 779         tp = (struct tftphdr *)buf;
 780         tp->th_opcode = htons((u_short)ERROR);
 781         tp->th_code = htons((u_short)error);
 782         for (pe = errmsgs; pe->e_code >= 0; pe++)
 783                 if (pe->e_code == error)
 784                         break;
 785         if (pe->e_code < 0) {
 786                 pe->e_msg = strerror(error - 100);
 787                 tp->th_code = EUNDEF;   /* set 'undef' errorcode */
 788         }
 789         strcpy(tp->th_msg, pe->e_msg);
 790         length = strlen(pe->e_msg);
 791         tp->th_msg[length] = '\0';
 792         length += 5;
 793         if (send(peer, buf, length, 0) != length)
 794                 syslog(LOG_ERR, "nak: %m");
 795 }
 796
 797 /* translate IPv4 mapped IPv6 address to IPv4 address */
 798 static void
 799 unmappedaddr(struct sockaddr_in6 *sin6)
 800 {
 801         struct sockaddr_in *sin4;
 802         u_int32_t addr;
 803         int port;
 804
 805         if (sin6->sin6_family != AF_INET6 ||
 806             !IN6_IS_ADDR_V4MAPPED(&sin6->sin6_addr))
 807                 return;
 808         sin4 = (struct sockaddr_in *)sin6;
 809         addr = *(u_int32_t *)&sin6->sin6_addr.s6_addr[12];
 810         port = sin6->sin6_port;
 811         memset(sin4, 0, sizeof(struct sockaddr_in));
 812         sin4->sin_addr.s_addr = addr;
 813         sin4->sin_port = port;
 814         sin4->sin_family = AF_INET;
 815         sin4->sin_len = sizeof(struct sockaddr_in);
 816 }
 817
 818 /*
 819  * Send an oack packet (option acknowledgement).
 820  */
 821 static void
 822 oack(void)
 823 {
 824         struct tftphdr *tp, *ap;
 825         int size, i, n;
 826         char *bp;
 827
 828         tp = (struct tftphdr *)buf;
 829         bp = buf + 2;
 830         size = sizeof(buf) - 2;
 831         tp->th_opcode = htons((u_short)OACK);
 832         for (i = 0; options[i].o_type != NULL; i++) {
 833                 if (options[i].o_request) {
 834                         n = snprintf(bp, size, "%s%c%d", options[i].o_type,
 835                                      0, options[i].o_reply);
 836                         bp += n+1;
 837                         size -= n+1;
 838                         if (size < 0) {
 839                                 syslog(LOG_ERR, "oack: buffer overflow");
 840                                 exit(1);
 841                         }
 842                 }
 843         }
 844         size = bp - buf;
 845         ap = (struct tftphdr *)ackbuf;
 846         signal(SIGALRM, timer);
 847         timeouts = 0;
 848
 849         (void)setjmp(timeoutbuf);
 850         if (send(peer, buf, size, 0) != size) {
 851                 syslog(LOG_INFO, "oack: %m");
 852                 exit(1);
 853         }
 854
 855         for (;;) {
 856                 alarm(rexmtval);
 857                 n = recv(peer, ackbuf, sizeof (ackbuf), 0);
 858                 alarm(0);
 859                 if (n < 0) {
 860                         syslog(LOG_ERR, "recv: %m");
 861                         exit(1);
 862                 }
 863                 ap->th_opcode = ntohs((u_short)ap->th_opcode);
 864                 ap->th_block = ntohs((u_short)ap->th_block);
 865                 if (ap->th_opcode == ERROR)
 866                         exit(1);
 867                 if (ap->th_opcode == ACK && ap->th_block == 0)
 868                         break;
 869         }
 870 }